Distance dominant intraocular lens

ABSTRACT

An intraocular lens includes a base refractive structure having anterior and posterior surfaces that are shaped for producing a first optical power and a diffractive structure formed in one of the surfaces of the base refractive structure including overlapping first and second diffractive patterns over a common aperture for producing second and third optical powers. The second optical power is an uneven division of the third optical power. The first and second diffractive patterns have respective step heights that are separately varied as a function of radial distance from the optical axis over the common aperture.

TECHNICAL FIELD

This invention generally relates to multi-focal intraocular lenses andparticularly such lenses with compound diffraction gratings onrefractive bases with aspheric surfaces.

BACKGROUND OF THE INVENTION

Natural crystalline lenses in the human eye accommodate power variationsrequired to support a range of focal distances from near to far(distance) vision by changing shape. Replacement of the crystallinelenses with manufactured intraocular lenses (IOLs), such as duringcataract surgery, has long resulted in a loss of such accommodation forsupporting a range of focusing options. Monocular IOLs require patientsto choose a given focal power, such as for supporting near or farvision, and to use eyeglasses to focus at some other distance.

Multi-focal IOLs are typically designed to provide two or more annularzones that provide different optical powers, typically using refractiveand/or diffractive focusing mechanisms. Each of the annular zones has adifferent aperture and the outer zones can be truncated by changes inpupil size. Other multi-focal IOLs form diffractive structures over theentire lens and use different diffractive orders to divide light energyinto different focal powers. A base refractive lens shaped to supportfar vision, for example, can be combined with one or more diffractivestructures to provide intermediate and near vision. Compound diffractiongratings with harmonically related features have also been used todivide light energy into different optical powers where the second orderof the lower power grating matches the first order of the higher powergrating to make more efficient use of the diffracted light.

SUMMARY OF INVENTION

According to an aspect of the present disclosure, a tri-focal IOL isenvisioned with a distance vision dominant energy distribution under lowlight conditions while still providing good near and intermediate visionunder bright light conditions. Diffractive profiles supporting near andintermediate vision can be apodized as a function of radial distance sothat as the user's pupil opens under mesopic conditions, the proportionof light directed into the optical powers supporting near andintermediate vision is reduced leaving more light directed through theoptical power supporting distance vision. This increase in distanceenergy with reduced near/intermediate energy under mesopic conditions isexpected to minimize unwanted visual effects. The increased distributionof light supporting distance vision with pupil enlargement can be drawnprimarily from a reduction in the energy devoted to near vision so thatthe energy devoted to intermediate vision provides a transition zonebetween distance and near vision over the considered range of pupilenlargement.

Preferably, the diffractive profiles are superimposed on a baserefractive surface, e.g., the anterior surface of the IOL, sharing acommon central axis with the diffractive profiles. The opposite siderefractive surface, e.g., the posterior surface, is preferably similarlycentered. Together, the opposite side surfaces are fashioned withrefractive curves to provide the optical power necessary to supportdistance vision and can also be fashioned with aspheric profiles tocompensate for anticipated spherical aberration in the overall opticalsystem of the eye. The diffractive profiles divide optical energy intoadditional focal powers.

The diffractive profiles can be formed by superimposing differentdiffractive patterns for supporting near and intermediate vision throughfirst and second orders of diffraction while preserving distance visionthrough the zero diffractive order. First order diffraction through afiner pitch diffractive pattern supports the increased focusing power ofnear vision, and first order diffraction through a coarser pitchdiffractive pattern supports the lesser focusing power of intermediatevision. However, instead of harmonically relating the two diffractivepatterns so that the features of the two patterns periodically overlap,the progressive periodicities of the two patterns depart from suchregularity so that the optical power contributed by the second order ofthe coarser pitch pattern departs slightly from the optical powercontributed by the first order of the finer pitch diffractive pattern toextend the depth of focus associated with near vision. Thus, instead ofusing the second order of the coarser pitch diffractive pattern tocontribute to the near power otherwise provided by the finer pitchdiffractive pattern, the second order of the coarser pitch diffractivepattern increases the depth of focus associated with the near power.

The diffractive features of each of the two superimposed diffractivepatterns preferably define annular zones separated by vertical stepswith parabolic profiles or their circular approximations extendingbetween the steps. While the two diffractive patterns are superimposedto produce a composite diffractive profile, the step heights of the twodiffractive patterns can be separately adjusted in accordance with thediffraction efficiencies of the two patterns to distribute optical powerin desired amounts among the near, intermediate, and far focusingoptions. In addition, the step heights are also preferably varied as afunction of radial distance from the optical axis to vary thedistributions of optical energy among the near, intermediate, and farfocusing options with increasing pupil size. Two different apodizationfunctions are preferably applied over different radial distances fromthe optical axis.

An intraocular lens in accordance with this disclosure includes a baserefractive structure having anterior and posterior surfaces that areshaped for producing a first optical power and a diffractive structureformed in one of the surfaces of the base refractive structure includingoverlapping first and second diffractive patterns over a common aperturefor producing second and third optical powers. The second optical poweris preferably an uneven division of the third optical power.

The first optical power is preferably conveyed through zero orderdiffraction of the first and second diffractive patterns for forming adistance focus. The second and third optical powers are preferablyconveyed through first order diffractions of the first and seconddiffractive patterns forming in combination with the first optical powerrespective intermediate and near foci. Preferably, the first and seconddiffractive patterns have non-harmonic periodicities so that a secondorder diffraction through the first diffractive pattern produces a focusthat is slightly offset from the near focus for extending an effectivedepth of the near focus.

The first and second diffractive patterns are preferably centered abouta an optical axis of the base refractive structure and have respectivestep heights that are separately varied as a function of radial distancefrom the optical axis over the common aperture. The step heights of thesecond diffractive pattern are preferably varied more than the stepheights of the first diffractive pattern as a function of the radialdistance from the optical axis. the step heights of at least one of thediffraction patterns preferably vary in a non-progressive manner

The distance focus is preferably arranged to receive an increasingportion of optical energy transmitted through the common aperture as afunction of the radial distance from the optical axis. The increasingportion can be derived more from a corresponding decrease in the opticalenergy received by the near focus than a corresponding decrease in theoptical energy received by the intermediate focus.

An intraocular lens in accordance with this disclosure can also bedescribed as having a base refractive structure with anterior andposterior surfaces that are shaped for producing a first optical powerthat directs incident light through a distance focus and a diffractivestructure formed in one of the surfaces of the base refractive structureover a common aperture for producing second and third optical powersthat in combination with the first optical power direct incident lightthrough respective intermediate and near foci. The diffractive structureincludes a first diffractive pattern for producing the second opticalpower through a first order diffraction and a second diffractive patternfor producing the third optical power through a first order diffraction.The first and second diffraction patterns are superimposed over thecommon aperture and have non-harmonic periodicities so that a secondorder diffraction through the first diffractive pattern extends thefocal depth of the near focus.

The distance focus is preferably arranged to receive an increasingportion of optical energy transmitted through the common aperture as afunction of radial distance from the optical axis. The increasingportion of the optical energy can be derived more from a correspondingdecrease in the optical energy received by the near focus than acorresponding decrease in the optical energy received by theintermediate focus. The step heights of the second diffractive patternare preferably varied more than the step heights of the firstdiffractive pattern as a function of the radial distance from theoptical axis. The functions for defining step height can differ overdifferent ranges of the radial distance so that the step heights of atleast one of the diffraction patterns vary in a non-progressive mannerwith the radial distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-section of an intraocular lens (IOL) with adiffractive profile on an anterior surface.

FIG. 2A plots the profile of one of two overlapping diffractive patternsfor producing a near focus.

FIG. 2B plots the profile of the other of the two overlappingdiffractive patterns for producing an intermediate focus.

FIG. 2C plots a combined profile of the two overlapping diffractivepatterns.

FIG. 3 plots the profile of the anterior surface of the IOL in which thediffractive profile is superimposed on the refractive profile of thebase refractive surface.

FIG. 4A contains Table B1 listing radial locations and apodized stepheights of each of the zones in the diffractive pattern for producingthe near focus.

FIG. 4B contains Table B2 listing radial locations and apodized stepheights of each of the zones in the diffractive pattern for producingthe intermediate focus.

FIG. 5 plots optical energy distributions among, near, intermediate, andfar (distance) focal zones over a range of pupil sizes.

FIG. 6A plots through focus MTF values over a range of defocus distancesat a 3 mm aperture.

FIG. 6B plots through focus MTF values over a range of defocus distancesat a 4.5 mm aperture.

FIG. 7A plots representative theoretical through frequency MTF curves atthe far focus for a 3 mm aperture.

FIG. 7B plots representative theoretical through frequency MTF curves atthe intermediate focus for the 3 mm aperture.

FIG. 7C plots representative theoretical through frequency MTF curves atthe near focus for the 3 mm aperture.

FIG. 7D plots representative theoretical through frequency MTF curves atthe far focus for a 4.5 mm aperture.

DETAILED DESCRIPTION OF THE INVENTION

An intraocular lens (IOL) 10 shown in FIG. 1 has a base refractivestructure 12 in a generalized form of a lens including a convex anteriorsurface 14 and a convex posterior surface 16 but is intended to berepresentative of IOLs of a variety of known forms including refractivestructures with various combinations of concave, convex and planarsurfaces. In addition, while the anterior and posterior surfaces 14 and16 appear as spherical surfaces, both surfaces 14 and 16 are preferablyaspheric surfaces centered about a common optical axis 18. A diffractivestructure 20, which is intended to be constructed in accordance withvarious embodiments of this disclosure, is superimposed on the anteriorsurface 14 of the IOL 10 and is incorporated into the shape of theanterior surface 14.

Both the refractive profile contributed by the base refractive structure12 and the diffractive profile contributed by the diffractive structure20 in the anterior surface 14 are axially symmetric, and therefore, asuperposition of the base refractive curve B(r) and a diffractive curveD(r), with “r” being the radial distance from optic central axis, candefine the entire optical region of the anterior surface 14. The baserefractive curve B(r) can be varied in accordance with other refractiveparameters of the IOL 10, including the shape of the posterior surface16 and the thickness of the base refractive structure 12, to support arange of base optical powers intended for distance vision while alsoincorporating an appropriate conic constant to adjust for sphericalaberration.

However, for manufacturing purposes, the base refractive profile of theanterior surfaces is preferably held constant over limited ranges ofoptical powers and the base refractive profile of the posterior surfaceis varied to adjust optical power within the limited ranges. Theposterior conics were developed to effect an approximately equalnegative spherical aberration over the entire range of optical powers.U.S. Pat. No. 8,535,376 entitled “Aspheric Lenses and Lens Family” ishereby incorporated as a reference for fashioning a family of IOLs witha desired amount of spherical aberration.

The diffractive structure 20 divides the optical energy passing throughthe IOL 10 into multiple diffraction orders that result in multiplefocal zones. The zeroth diffraction order conveys the optical power ofthe base refractive structure 12 for the distance focus. Intermediateand near foci are provided by the first and second diffraction ordersthat contribute additional amounts of optical power beyond the opticalpower of the base refractive structure 12. The diffractive surface curveD(r) is derived from the superposition of two diffractive patterns suchas shown in FIGS. 2A-2C. The patterns are plotted in step heights over arange of radial distances from the optical axis 18 (with units inmillimeters). The diffractive pattern of FIG. 2A contributes 3.1 D(diopters) of additional optical power through the first diffractionorder for producing the near focus, the diffractive pattern of FIG. 2Bcontributes 1.6D (diopters) of additional optical power through thefirst diffraction order for producing the near focus. The second orderof the diffractive pattern of FIG. 2B contributes 3.2D (diopters) ofadditional optical power, which provides a closely spaced near focus toincrease the depth of focus associated with the near power. Thus, theoptical power contributed by the coarser pitch diffractive pattern ofFIG. 2B is an uneven division of the optical power contributed by thefiner pitch diffractive pattern of FIG. 2A. The departure from aharmonic relationship between the two diffractive patterns shown inFIGS. 2A and 2B is even more apparent when the diffractive patterns areplotted as functions of the radial distance squared such that each ofthe diffractive patterns have a constant pitch.

Each of the diffractive patterns for contributing 3.1 D and 1.6D ofadditional optical power comprise zones separated by vertical steps witha parabolic profile between the start and end points of each zone. Theradial locations of the zonal end points are given by:

r _(p)=√{square root over (2pfγ)}

where “p” is the zone number, “f” is the focal length of the diffractiveadd power, and “γ” is the design wavelength.

The superposition of the final composite diffractive profile D(r) asshown in FIG. 2C on the base refractive curve B(r) results in a profileof the kind shown in FIG. 3 . The profile is plotted in terms of stepheight over a range of radial distances from the optical axis 18. Thediffractive profile steps apparent in FIG. 2C are about two orders ofmagnitude smaller than the refractive surface sag.

For purposes of achieving a distance vision dominant energy distributionunder low light conditions as well as providing good near and functionalintermediate vision under bright light conditions, the diffractiveprofile is apodized by modifying the diffractive step heights for the3.1 D and 1.6D patterns.

The diffractive step heights are given by:

$h = \frac{\gamma\varepsilon}{\left( {n_{l} - n_{a}} \right)}$

where, “h” is diffractive step height (unapodized); “∈” is diffractionefficiency; “γ” is design wavelength; “n_(l)” is the lens materialrefractive index and “n_(a)” is aqueous refractive index.

An apodization function example for the radial range 0≤r≤3 mm is:

$e^{- {(\frac{r}{1.8})}^{2}}$

An apodization function example for the radial range r>3 mm is:

$e^{- {(\frac{r}{3})}^{2}}$

The resulting diffractive profile radial locations for each zone edgeand apodized step height for the diffractive patterns of FIGS. 2A and 2Bare listed in the respective Tables B1 and B2 of FIGS. 4A and 4B. As aresult of the different functions spanning different ranges of radialdistance, the apodized step heights of the two diffractive profilepatterns vary in a non-progressive manner with height discontinuitiesappearing between the sixth and seventh zones of the 3.1 D profile andbetween zones three and four of the 1.6D profile.

FIG. 5 shows an energy balance diagram, developed using numericalsimulations. Each of the three lines 30, 32 and 34 plots a respectiveportion of the optical energy distributed among the respective far(distance), intermediate, and near focal zones over a range of pupildiameters from 2 mm to 4.5 mm. Beginning at a pupil diameter ofapproximately 2 mm the portion of the optical energy delivered to thenear focal zone is approximately equal to the portion of the opticalenergy delivered to the far focal zone but for pupil diameters fromapproximately 2.5 mm to 4.5 mm the portion of the optical energydelivered to the far focal zone increases while the portion of theoptical energy delivered to the near focal zone decreases. The portionof the optical energy delivered to the intermediate focal zone starts ata lower level than the portions of the optical energy delivered to thenear and far focal zones the pupil diameter of approximately 2 mm butdeclines over the range from approximately 2.5 mm to 4.5 mm pupildiameters at a shallower rate than the decline of the energy deliveredto the near focal zone over the same range. Thus, most of the increasein optical energy gained by the far focal zone over the range fromapproximately 2.5 mm to 4.5 mm pupil diameters results from a decreasein the portion of energy delivered to the near focal zone. Theintermediate focal zone provides a stable transition between the varyingenergy deliveries to the near and far focal zones.

Representative theoretical through focus MTF curves for a 20D base powerIOL, at 3 mm and 4.5 mm apertures, are plotted in FIGS. 6A and 6B. TheMTF values are plotted over a range of positive and negative defocusdistances along the optical axis. The plots contemplate a 50 lp/mm, ISOModel eye 0.15 μm SA and the IOL with −0.15 μm SA in the ISO Model Eye1.

Representative theoretical through frequency MTF curves for the 20D IOLat the far (distance), intermediate, and near foci at a 3 mm apertureare respectively plotted in FIGS. 7A, 7B, and 7C. FIG. 7D similarlyplots the far focus at a 4.5 mm aperture over an extended range ofspatial frequencies.

1. An intraocular lens comprising: a base refractive structure havinganterior and posterior surfaces that are shaped for producing a firstoptical power; a diffractive structure formed in one of the surfaces ofthe base refractive structure including overlapping first and seconddiffractive patterns over a common aperture for producing second andthird optical powers; and the second optical power being an unevendivision of the third optical power; wherein the first and seconddiffractive patterns convey the first optical power through zero orderdiffraction for forming a distance focus; the first and seconddiffractive patterns provide for producing the second and third opticalpowers through a first order diffraction for forming in combination withthe first optical power respective intermediate and near foci; and thediffractive structure is centered about an optical axis of the baserefractive structure, and the first and second diffractive patterns havestep heights configured to be separately varied such that the distancefocus will receive an increasing portion of optical energy transmittedthrough the common aperture as a function of radial distance from theoptical axis, and the increasing portion of the optical energy will bederived more from a corresponding decrease in the optical energyreceived by the near focus than a corresponding decrease in the opticalenergy received by the intermediate focus.
 2. The intraocular lens ofclaim 1 in which: the first and second diffractive patterns havenon-harmonic periodicities so that a second order diffraction throughthe first diffractive pattern produces a focus that is slightly offsetfrom the near focus for extending an effective depth of the near focus.3. (canceled)
 4. The intraocular lens of claim 1 in which the stepheights of the second diffractive pattern are varied more than the stepheights of the first diffractive pattern as a function of the radialdistance from the optical axis.
 5. (canceled)
 6. The intraocular lens ofclaim 1 in which the step heights are varied as functions of theirradial distance from the optical axis, and the functions differ overdifferent ranges of the radial distance.
 7. The intraocular lens ofclaim 6 in which the step heights of at least one of the diffractionpatterns vary in a non-progressive manner with the radial distance. 8.An intraocular lens comprising: a base refractive structure havinganterior and posterior surfaces that are shaped for producing a firstoptical power that directs incident light through a distance focus; adiffractive structure formed in one of the surfaces of the baserefractive structure over a common aperture for producing second andthird optical powers that in combination with the first optical powerdirect incident light through respective intermediate and near foci; thediffractive structure including a first diffractive pattern forproducing the second optical power through a first order diffraction;the diffractive structure including a second diffractive pattern forproducing the third optical power through a first order diffraction; andthe first and second diffraction patterns being superimposed over thecommon aperture and having non-harmonic periodicities so that a secondorder diffraction through the first diffractive pattern extends thefocal depth of the near focus; wherein the diffractive structure iscentered about an optical axis of the base refractive structure, and thefirst and second diffractive patterns have step heights configured to beseparately varied such that the distance focus will receive anincreasing portion of optical energy transmitted through the commonaperture as a function of radial distance from the optical axis, and theincreasing portion of the optical energy will be derived more from acorresponding decrease in the optical energy received by the near focusthan a corresponding decrease in the optical energy received by theintermediate focus.
 9. (canceled)
 10. The intraocular lens of claim 8 inwhich: the step heights of the second diffractive pattern are variedmore than the step heights of the first diffractive pattern as afunction of the radial distance from the optical axis.
 11. Theintraocular lens of claim 10 in which the step heights are varied asfunctions of their radial distance from the optical axis, and thefunctions differ over different ranges of the radial distance.
 12. Theintraocular lens of claim 11 in which the step heights of at least oneof the diffraction patterns vary in a non-progressive manner with theradial distance.
 13. The intraocular lens of claim 8 in which the secondoptical power contributed by the first diffractive pattern isapproximately 1.6 diopters and the third optical power contributed bythe second diffractive pattern is approximately 3.1 diopters.
 14. Theintraocular lens of claim 8, wherein two different apodization functionsare applied over different radial distances from the optical axis forvarying the step heights of the first and second diffraction patterns asa function of radial distance.
 15. The intraocular lens of claim 1,wherein two different apodization functions are applied over differentradial distances from the optical axis for varying the step heights ofthe first and second diffraction patterns as a function of radialdistance.